Air purifying respiratory protective devices currently used by the military for protection against chemical and biological contaminants impose a substantial physiological burden on the wearer. These respirators (masks) are difficult to wear for prolonged periods because they are relatively bulky and heavy, have high breathing resistance, impair vision and communications, cause thermal stress, physical discomfort, and degrade job performance. The demands placed on respiratory protection equipment for use by the crews of military vehicles: e.g., land and/or sea vehicles and aircraft, are even greater, due to the limitations on the size or bulk of such crew masks in crowded crew cabins, and the need to avoid fogging of the lenses, and crew person exhaustion from heat buildup, physical discomfort and/or respiratory effort.
Thus, crew mask respirator systems for protecting vehicle crews must be optimized for minimal bulk and weight, in order to readily fit within the limited crew space provided. In addition, crew masks must be optimized to provide a sufficient flow of purified air for respiration and comfort, e.g., minimizing lens fogging, heat stress, respiratory effort and excessive pressure by the mask seals on contacted parts of the face and/or head.
Previous efforts to provide crew masks include the U.S. Army M45 (Aircrew) and M42 (Combat Vehicle) masks. These masks use a standard six point suspension system and an intern periphery design. The artisan will appreciate that an “intern” periphery provides that the contact point/seal between the mask and the skin of the user is provided by an inwardly turned mask edge. However, the M45 has no powered blower system due to weight and logistic concerns. While the M45 provides adequate unblown protection and defogging properties, this crew mask is reported to be very uncomfortable when used in combination with helmet systems, e.g., aircrew helmets, due to the harness buckles and the presence of the intern seal in the forehead area, where a crew helmet can press the seal into the forehead. In addition, the lack of a powered blower system results in high breathing resistance, adding to crew fatigue.
In an alternative approach, the U.S. Air Force AERP mask system eliminates the face seal, in favor of a neck seal design. In addition, both the U.S. Army M48/M49 and the U.S. Air Force AERP use a dual canister blower system for providing the overpressure needed for protection against inward diffusion of toxic agents, and to provide additional airflow for keeping the lenses free of moisture or fog. Existing blowers are built to provide for air flow rates of approximately 4 cubic feet per minute CFM and attendant overpressure. Given the need for an air flow of approximately 4 CFM, the presently employed blowers for all current crew mask systems are sub-optimal in size and bulk.
Thus, there remains a need in the art for a crew mask for protection against chemical or biological toxic agents that provides a comfortable face seal and helmet interface and an optimized size and bulk of the equipment, while still providing adequate protection and defogging in the confines of a vehicle.